High temperature implement



July 10, 1962 T. s. LASZLO HIGH TEMPERATURE IMPLEMENT Filed April 21, 1960 3 //////////////AW COOLANT i A/COOLANT-IN \\\\EE\\\ \\\\\\\\i\ \l9 W- 1\\\\\\\N OUT TIBOR S LASZLO INVENTOR.

BY ,4/ M 49m- ATTORNEYS United States Patent 3,043,972 HIGH TEMPERATURE IMPLEMENT Tlbor Laszlo, Melrose, Mass., assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Apr. 21, 1960, Ser. No. 23,698

* 8 Claims. (Cl. 313-32) This invention relates to a high temperature implement and, in particular, to an electrode for an arc apparatus and high temperature probes.

In plasma generators and arc welding equipments erosion of the center electrode are an important limitation in the reliability and usefulness of these equipments. In order to generate the extremely high temperatures desired in arc equipments the center electrode, typically the oathode, is required to conduct extremely high currents, in the order of 1000 amperes. Accordingly, the electrodes are required to operate in extremely high temperature environments generated by the arc and by the power dissipated internally. The life of prior art electrodes is short, in the order of two to three hours of continuous operation. Frequent replacement accompanied by costly downtime is required.

Where the arc device is used as a research tool the erosion of the electrode has been found to be detrimental. The eroding material is deposited on the specimen being subjected to the plasma thus creating nonhomogeneous surfaces. In addition, the electrode material often reacts with the specimen being tested to the detriment of the test results.

In industrial coating procedures, the eroding material tends to contaminate the coating, unless of course, the electrode material is the same as the coating material. It is quite obvious, however, that this condition limits the scope of the arc coating apparatus.

A third important limitation, of are devices incorporating electrodes which readily erode, is the variation in spacing between the anode and cathode electrode brought about by the steady erosion of the cathode electrodematerial. As is well known, are current and potential, and temperature generated by the arc vary with the spacing between the cathode and electrode. The current supplied to the arc must therefore be closely regulated to compensate for the variation in spacing to maintain a constant arc environment.

To reduce erosion of high temperature implements, they are usually forced cooled. That is to say, a coolant is supplied to the implement to carry the heat developed therein away. In many instances this procedure has been satisfactory. However, where the implement is made of tungsten, forced cooling has been found to be impractical because tungsten becomes porous at high temperatures and coolants, particularly water, permeate the tungsten, Heretofore, practitioners have resorted to other materials in place of tungsten. However, with the advent of extremely high temperatures, in the order of 15,000 to 20,000 F., developed in plasma generating devices, the practitioners have begun to take another look at tungsten. The reason, of course, is obvious; tungsten has the highest melting point of any known metal. Its porosity, how ever, has limited its use in certain shapes of electrodes and probes which include forced cooling means. A solution making it possible t use tungsten in high temperature implements is presented herein.

In many types of arc devices the cathode takes the shape of an elongated member commonly called a pencilshaped electrode; the length of the electrode is substantially larger than its diameter. This invention is directed particularly, but without limitation thereto, towards an improvement in pencil-shaped electrodes, or pencilshaped high temperature implements for that matter.

It is an object of the invention to provide a high temperature implement, typically an arc electrode or a high temperature probe which avoids the disadvantages and limitations of prior art devices of this type.

It is another object of the invention to provide a high temperature implement which incorporates an improved form of forced cooling.

It is still another object of the invention to provide a tungsten high temperature implement which includes provision for using tungsten material at temperatures at which the tungsten becomes porous.

It is still another object of the invention to provide a high temperature forced cooled implement comprising a refractory tip and a lining means for preventing the coolant from coming into direct contact with the refractory tip.

Other objects of the invention are to provide:

(1) A high temperature implement which is relatively simple in construction;

(2) A high temperature implement which utilizes a tungsten tip formed by machining processes;

(3) An are electrode and/or high temperature probe which have a relatively long life;

(4) An arc electrode and/or high temperature probe 1 that are very efficient heat transfer devices; and

(5) A high temperature implement having an easily replaceable refractory tip.

In accordance with the invention a high temperature implement comprises a tipformed from refractory material and lining means. The refractory material comprises a thin-walled sleeve terminating in a closed end and an open end, all of which define a recess therein. The lining means comprises inner and outer co-axial tubular means for carrying a coolant to and from the refractory tip; the outer tubular means being shaped to mate intimately with the surfaces of the refractory tip defining the recess. One end of the outer tubular means is closed and dimensioned to abut the closed end of the refractory tipthe bottom of the recessfor preventing the coolant from coming into direct contact with the refractory tip.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is an embodiment of an arc electrode incorporating the novel features of the present invention; and

FIGURE 2 is an exploded view of another are electrode construction incorporating the novel features of the present invention.

Referring to FIGURE :1 of the drawings there is illustrated an arc electrode embodying the novel features of the present invention. The are electrode, generally d@Sig-: nated 10, comprises a tip 11 formed from a refractory material preferably tungsten. The refractory tip 11 includes thin peripheral walls 13 terminated at one end by a substantially conical portion 17. A central cylindrical recess 12 is defined by the inside surfaces 15 and .16 of the walls 13 and end 17 respectively. The shape of end 17 described and illustrated is not to be considered limiting. To efficiently carry away heat from the end 17, its wall thickness and the distance between the outside surface of end 17 and recess 12 should be made as small as possible. This will be discussed further hereinafter.

The are electrode 10 also includes lining means for the walls of recess 12 for carrying coolant to and from the tip 11. The lining means, generally designated '18, includes inner and outer sleeves 1 9 and 21 respectively, both of which are co-axial with the refractory tip. The sleeves 19 and 21 are preferably formed from copper which 3 is an excellent heat conductor and remains nonporous at high temperatures.

The outer sleeve 21 includes a portion of a reduced diameter 22 which is constructed to mate intimately with the walls of recess 12 and is inserted in recess 12. The portion of reduced diameter 22 is terminated in a closed end 23 which mates and abuts against the surface 16 of the recess 12. The inner sleeve 19 terminates in an open end 24 which is spaced a finite distance from the end 23 of the outer sleeve 21. As shown in FIGURE 1, the coolant, usually water is fed into the inner sleeve 19 and passes through the open end 24 and impacts against the closed end 23 of the outer sleeve 21. The coolant reverses its direction and passes through the space between the inner and outer sleeves 19 and 21 respectively and finally emerges from the electrode.

In order to insure an efficient transfer of heat from the refractory tip to the lining means 18, the outer diameter of the portion of reduced diameter 22 is very nearly the same as the diameter of recess 12. In addition, the cooling means 18 is secured to the refractory tip 11 by means of a high temperature brazed joint 25 shown at their interface. Silver solder or an equivalent is used to make the brazed joint. 7

Referring now to FIGURE 2 of the drawings there is shown another form of an arc electrode embodying the principlesof the present invention. Like parts in FIG- URE 2 carry the same number designations as their FIG- URE 1 counterparts. In FIGURE 2 the refractory tip 11 includes on the surface of recess '12 and ends 14 a copper coating 27. The coating 27 is preferably electrodeposited on tip 11, but other suitable coating processes such as spraying or precipitation may be used. The thickness of the copper coating 27 is not critical, the only requirement being that it be thick enough so that it can be considered continuous at high temperatures. The lining means includes an inner and outer sleeve .19 and 21 respectively, the inner sleeve projecting from an open end 28 of the outer sleeve 21. The inner diameter of the outer sleeve 21 and the inner diameter of the plated surfaces are substantially equal. (The mating portions of the refractory tip 11 and the outer sleeve 21 are likewise complementary.

To assemble the arc electrode it is merely necessary to abut the open end 28 against the complementary copper surface 29 and secure these surfaces by means of a hard solder as described above. The protruding length of the inner cylinder 19 is dimensioned so that the terminal end 24 thereof, is spaced from the bottom surface 16 of the recess 12.

The FIGURE 2 embodiment is the preferred construction for several reasons. Maximum contact in the interface between the tip 11 and the copper coolant tubes is assured. The wall thickness of the copper in contact with the tip 11 is minimal. Both of the foregoing factors improve heat transfer to the coolant. The coated construction is also simpler to make.

To properly design an electrode or a high temperature probe, several contradictory considerations must be compromised. For maximum heat transfer, thus maximum cooling, the distance separating the source of heat and the coolant should be as small as possible. However, since the electron immersion ability of materials increases with increasing temperature, it is desirable to operate an arc electrode at as high a temperature as possible. Similarly, in a high temperature probe it is not desirable to provide an excess amount of cooling since a principal consideration is that the probe in no way influences its surroundings. fIhe coolant need only prevent deterioration of the probe.

A third consideration is the vapor pressure of the ma? terial as a function of temperature since it affects the lifeof the tip; Erosion due to evaporation of the tip materialincre'ases with increasing temperature.

Fortunately, none of the aforementioned factors are overriding and a suitable design may be arrived at by the A. application of thermodynamic principles. The parameters of one very satisfactory arc electrode, capable of carrying in the order of 1000 amperes are outlined below.

Inches Over-all diameter .385 Recess diameter .25 Peripheral wall thickness .0625 The dimensionD (FIGURE 1) .50 Copper liner wall thickness .0925

The principal advantage of the aforementioned construction over prior electrodes is that the coolant, water for example, does not come in contact with the refractory tip. It is well known that copper does not become porous at elevated temperatures and thus the coolant is contained within the passage defined by the inner and outer sleeves 19 and 21 respectively. The heat generated in the refractory tip 11 is carried to the coolant in an efficient manner. It will be noted that the walls of the refractory tip 11 are relatively thin thus reducing the distance heat must travel to reach the coolant. The interface between the lining means and the refractory tip comprises a continuous metallic surface thus maximizing heat transfer across it. The use of a copper lining means also adds to the efliciency with which heat can be carried from the refractory tip since it is well known that copper is one of the better heat conducting mediums.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved Without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. A high temperature implement comprising: a tip formed from a refractory material including a peripheral wall, a closed end and an open end, the inside surfaces of the peripheral wall and the closed end defining a recess; nonporous lining means for carrying a coolant to and from said tip terminating in a closed end portion for preventing direct contact between the tip and the coolant, the closed end portion being shaped to mate with the recess and being inserted therein.

2. A high temperature implement as claimed in claim 1 in which the refractory material is tungsten.

3. A high temperature implement as claimed in claim 1 in which said closed end portion and said tip are brazed at their interface.

4. A high temperature implement comprising: a tip formed from a refractory material including a peripheral wall, a closed end and an open end, the inside surfaces of the peripheral wall and the closed end defining a recess; a coating of nonporous material deposited on the inside surfaces defining the recess and the open end; and lining means for carrying a coolant to and away from the recess secured to the coated end in fluid communication with said coated inside surfaces.

5. A high temperature implement as claimed in claim 4 in which said coating is electrodeposited copper.

6. A high temperature implement as defined in claim '4 in which said lining means includes an outer sleeve, one end of which is secured in an abutting relationship with the coated open end and an inner sleeve spaced from the outer sleeve and extending into the recess and terminating adjacent to, but spaced from the coated closed end surface.

7. A high temperature implement as defined in claim 4 in which said sleeves comprise copper tubing.

8. A hightemperature implement comprising a cylindrical refractory tip having a conical end, an open end and thin peripheral walls defining a recess therein, an

end portion shaped to mate with the surfaces defining the 7 References Cited in the file of this patent UNITED STATES PATENTS 2,098,315 Sharp Nov. 9, 1937 2,362,816 Harker Nov. 14, 1944 2,821,650 Zunick et a1. Jan. 28, 1958 

